A two-step recognition fluorescent probe for ultra-wide range detection of SO2 in food and water samples

Bisulfite/sulfite has been approved as a worldwide food additive. Improper use of HSO₃⁻/SO₃²⁻ in food may cause great harm to the human body. Due to the diversity and complexity of food samples, developing universal method with broad detection range to meet practical needs is of great challenge and significance. Herein, for the first time a two-step recognition strategy was employed for probe construction, and a representative coumarin-hemicyanine based fluorescent probe CouXZ showed simultaneously linear response to HSO₃⁻/SO₃²⁻ of both low-level (0–50 μM) and high-level (100–700 μM), with good selectivity and fast response. Based on its ultra-wide range sensing property, CouXZ was successfully applied to determine SO₂ residue in 17 food samples and 7 liquid samples without complex sample treatment. Moreover, CouXZ coated test strips was facilely prepared to establish portable handheld UV lamp assisted smartphone sensing platform, exhibiting on-site quantitative analysis with good reliability and accuracy. In a word, the two-step recognition strategy could meet integrated detection needs of differentiated samples, proving its powerful and extensive sensing applications.